1. Field of the Invention
This invention concerns a method of manufacturing molten metal iron from iron oxide-containing material by using a rotary hearth furnace.
2. Description of the Related Art
A method of manufacturing a molten metal iron at a reduced cost by a rotary hearth furnace in a relatively simple facility and with less installation cost by using an inexpensive carbon material such as coal as a reducing material has been adopted in recent years, instead of a blast furnace method or as a method supplementary to the blast furnace method.
The molten metal iron is manufactured, for example, by a method reducing under heating a mixture of a powdery iron material and a solid powdery reducing agent in a rotary hearth furnace to produce a reduced iron, charging the mixture into a melt-reducing furnace and melting and reducing the same by using carbon material and oxygen to thereby removing slags. However, this method involves a problem that two steps of using the rotary hearth furnace and the melt-reducing furnace are required to increase the installation cost and the reduced iron has to be cooled upon discharge from the rotary hearth furnace so as to enable handling thus requiring additional energy in the melt-reducing furnace.
Then, there is a method of manufacturing a solid metal iron by reducing under heating the mixture on a rotary hearth furnace into a reduced iron, successively carburizing the reduced iron on the hearth with the carbon ingredient in the carbonaceous reducing material to melt the iron, separating the same into a metal iron and a slag ingredient and then cooling and solidifying the iron on the hearth, followed by recovery has been used. According to this method, the installation cost is lowered since the process can be conducted in one step but it still leaves a problem of high refining cost since additional energy is required for remelting the solid metal iron in a converter furnace or electric furnace upon refining.
This invention intends to provide a method of manufacturing a molten metal iron capable of discharging and recovering the molten metal iron separated from the slag on a rotary hearth furnace in the molten state as it is from the rotary hearth furnace without cooling and solidification.
In accordance with this invention, there is provided a method of manufacturing a molten metal iron by charging a starting material at least comprising a carbonaceous reducing material and an iron oxide-containing material into a rotary hearth furnace, reducing under heating the charged starting material into a solid reducing iron, carburizing the metal iron in the solid reduced iron with the carbon ingredient in the carbonaceous reducing material, thereby melting the metal iron, separating the slag ingredient contained in the starting material by the melting, and discharging the molten metal iron in the molten state as it is to the outside of the rotary hearth furnace for recovery, wherein a downward inclined surface is disposed at an angle of 3 to 30xc2x0 relative to the horizontal plane on the upper surface of a hearth of the rotary hearth furnace on which the starting material is placed, and the molten metal iron is discharged at a discharging position for the molten metal iron.
In the method of manufacturing the molten metal as described above, discharge ports for the molten metal iron passing from the upper surfaces to the lower surface of the hearth are disposed in plurality, an openable/closable valve is provided to each of the discharge ports, a downward inclined surface is disposed in the upper surface of the hearth toward the discharge port, and the molten metal iron is discharged from the discharge port by opening the valve when the discharge port reaches the discharging position along with rotation of the hearth.
In the method of manufacturing the molten metal as described above, the hearth may have the downward hearth on the inner circumference of the lateral width of the hearth or may have the downwarded hearth on the outer circumference thereof, a stationary dam having a recess to at least a position is disposed along the periphery on the lower side in the lateral direction of the hearth, and the molten metal iron is discharged through the recess, the hearth is divided circumferentially into a plurality of portion by partitions and the partition is formed of a refractory partition, formed by grooving the hearth, or formed by stacking a powdery carbonaceous material on the hearth.
In accordance with this invention, there is also provided a method of manufacturing molten metal iron in which the hearth comprises a plurality of circumferentially divided hearth portions and, when each of the divided hearth portions reaches the discharging position for the molten metal iron along with rotation of the hearth, the hearth portion is tilted to discharge the molten metal iron.
In the method of manufacturing the molten metal as described above, in which the slag remaining on the hearth is discharged out of the hearth by rotation after discharging the molten metal iron and before charging the starting material, the surface of the hearth is smoothed after discharging the molten metal and before charging the start material, a hearth protection material is charged onto the hearth after discharging the slag and before charging the starting material, the hearth protection material is charged on the hearth after the smoothing and before charging the starting material, and a mixture of previously mixing the hearth protection material with the powdery carbonaceous reducing material is charged instead of the hearth protection material.
In accordance with this invention, since the molten metal iron can be recovered continuously from the rotary hearth furnace in the molten state as it is with no cooling and solidification, molten metal iron with less fluctuation in the quality can be obtained by using only the rotary hearth furnace of a reduced installation cost continuously for a long period of time without requiring additional energy, thereby remarkably reducing the manufacturing cost for the molten metal iron.
Further, since slags remaining on the hearth can be removed to maintain the upper surface of the hearth smooth, heat can be conducted uniformly over the starting material to decrease the fluctuation of quality of the molten metal iron products.
Further, by laying the hearth protection material, peeling or roughening for the upper surface of the hearth can be prevented to extend the hearth life.
Furthermore, the charging facility can be decreased by charging the hearth protection material and the powdery carbonaceous reducing material in admixture as a floor laying material.